1. Field of the Invention
This invention relates to a method and apparatus for supplying molten metal in the manufacture of amorphous metal ribbons and, more particularly, to a method and apparatus for supplying molten metal to a tundish.
2. Description of the Prior Art
In recent years, amorphous metals have been attracting increasing attention because of their excellent magnetic properties. Amorphous metals are made into product form by continuously ejecting the molten metal stored, for instance, in a tundish through a fine slit at the nozzle tip onto the surface of a cooling roll rotating at high speed to rapidly cool and solidify the metal. The amorphous metal ribbons thus obtained are as thin as about 25 .mu.m. Accordingly, the rate of the metal supply onto the cooling roll surface is far lower than the rate at which molten metal is supplied from the tundish to the mold in ordinary continuous casting. It is therefore necessary to stabilize the amount of metal ejected through the fine slit of the nozzle by adjusting the head or level of the molten metal in the tundish. As such, it has been strongly desired to establish a method that permits implementing fine adjustment of the molten metal supply rate from a ladle or other container to the tundish.
FIG. 1 shows an example of a conventional method of supplying molten metal in the manufacture of amorphous metal ribbons. According to this method, molten metal M is supplied from a ladle 1 through a sliding nozzle 2 and a long nozzle 3 to a tundish 4. While maintaining the metal bath at a constant level, the molten metal M is ejected through a slit 7 of a nozzle 6 onto the surface of a rapidly rotating cooling roll 8 by adjusting a stopper 5.
The amount of molten metal M supplied from the ladle 1 to the tundish 4 is controlled by adjusting the opening of the sliding nozzle 2. In order to permit the makeup of the molten metal ejected through the nozzle slit 7, the opening of the sliding nozzle 2 must be quite small. However, the probability is quite strong that such a small opening might get clogged and thereby make it impossible to continue the supply of molten metal to the tundish in a short time.
Let it be assumed that the bath level H.sub.1 in the ladle 1 at the start of pouring is 20 cm, the distance H.sub.2 between the bath level in the tundish 4 and the bottom of the ladle 1 is 60 cm, the length and width of the nozzle slit 7 are 15 cm and 0.06 cm, and the discharge rate of molten metal from the nozzle slit 7 is 150 cm/sec. In order to replace the molten metal M discharged through the nozzle slit 7 from the ladle 1, the diameter of the hole provided in the plate of the sliding nozzle 2 must be about 7 mm. This is far smaller than the hole diameter of an ordinary sliding nozzle that stands at around 70 mm. Such a small hole might get clogged in a short time and therefore does not permit the continuous supply of a small quantity of molten metal from the ladle 1 to the tundish 4.
There is also another method that supplies molten metal from a ladle placed in a hermetically sealed container to a tundish that is connected to the ladle by a refractory U-tube by applying pressure on the surface of the molten metal in the ladle. Still another method employs a ladle and a tundish that are connected by a refractory U-tube equipped with a vacuum unit that draws the molten metal from the ladle for transfer into the tundish.
But these methods require costly equipment including a hermetically sealed container large enough to accommodate a ladle, a vacuum unit and a hermetically sealed refractory U-tube. Another drawback is the difficulty encountered in taking a prompt remedial measure against the metal leakage and other accidents.
Yet another method employing an electromagnetic pump is impractical because it involves too heavy a capital investment.
SUMMARY OF THE INVENTION
An object of this invention is to provide a method and apparatus for supplying molten metal in the manufacture of amorphous metal ribbons that are inexpensive and free from the aforementioned shortcomings of the conventional methods, and which permit continuous supply of a small amount of molten metal at a finely regulated rate.
Another object of this invention is to provide a method and apparatus for supplying molten metal in the manufacture of amorphous metal ribbons that assure a continuous supply of molten metal over a long period of time without being interrupted by nozzle clogging or metal leakage.
In manufacturing amorphous metal ribbons by ejecting molten metal from a nozzle attached to a tundish onto the surface of a rapidly moving cooling means, a method of supplying molten metal to the tundish according to this invention comprises the steps of pouring the molten metal from a ladle to an intermediate vessel, and thence to the tundish by way of a gas-lift pump.
An apparatus for supplying molten metal to a tundish according to this invention comprises an intermediate vessel adjoining the tundish and a gaslift pump that sends the molten metal from the intermediate vessel to the tundish. The molten metal is poured from a ladle into the intermediate vessel. The gas-lift pump comprises a pump proper that is placed over the intermediate vessel and tundish, with the inlet and outlet thereof opening into the intermediate vessel and tundish, respectively. Bubbles are supplied into the pump proper through the inlet thereof.
On account of the structure just described, the apparatus of this invention eliminates the need for providing a nozzle stopper or sliding plate between the ladle and tundish. Since the pump contains a mixture of air and liquid, a pipe of a larger diameter can be used than can be used in a system containing only liquid. This permits simplifying the structure of the molten metal supplying apparatus and reduces the likelihood of passage clogging.
The amount of metal supply can be controlled by adjusting the quantity of the bubbles supplied to the gas-lift pump. All this facilitates the supply of a slight quantity of molten metal at a finely controlled rate that is strongly desired in the manufacture of amorphous metal ribbons.